It is known to apply bismaleimides as bifunctional monomer or comonomer in compositions that are cured thermally, through an addition reaction or via radicals. The disadvantage of bismaleimides is that they are soluble in few other copolymerizable compounds. Thus, it has been found to be impossible to dissolve more 10 wt.-% of a bismaleimide in styrene. This is a disadvantage, because styrene is a monomer that can easily be polymerized, is inexpensive and, moreover, has a good chemical resistance. The object of the invention is the preparation of compositions and copolymers in which both styrene or an other copolymerizable compound and a substantial amount of a bismaleimide are used.